Feature: Implement data type comparison

In order to compare between data types, I am doing

```go
type (
CustomInterface interface {
Foo() string
}

CustomType1 struct { }
CustomType2 struct { }
)

func (ct1 CustomType1) Foo() {}
func (ct2 CustomType2) Foo() {}

...

func TestType(t testing.T) {
var i interface{} = &CustomType1{}

_, isType1 := i.(CustomType1)
_, isType2 := i.(CustomType1)

assert.Assert(t, isType1) // Success
assert.Assert(t, isType2) // Fail
}
```

It would be better if

```golang
customType := &CustomType1{}

assert.Assert(t, is.SameType(customType, CustomType1) // Success
assert.Assert(t, is.SameType(customType, CustomType2) // Fail
```